Micromirror devices have been developed because it can substitute for conventional optoelectronic devices. A phase-only piston-style micromirror was used for phase adaptive optics applications and a rotational micromirror was used to deflect a light. Most of these micromirrors have been controlled to have continuous displacements, which are determined at the equilibrium between electrostatic force and elastic force. The analog control is more complex than the digital or discrete control, and is not compatible with known semiconductor electronics technologies such as MOS, CMOS, etc. In addition, the micromirrors with continuous displacement actuated by electrostatic force undergo the classical snap-down phenomenon when the electric force exceeds the elastic force of mechanical structure. The snap-down phenomenon limits the translational and rotational ranges of a micromirror.
The high driving voltage is also another acute disadvantage in practical use of the micromirrors with continuous displacement actuated by electrostatic force. To be compatible with IC components, it is desired that micromirrors are operated at low voltage which is compatible with the circuit operation or control voltage.
In the prior art of micromirror array like Digital Micromirror Device in U.S. Pat. Nos. 4,566,939, 5,083,857, and 6,232,936, each micromirror is actuated by digital control of a voltage. It has large rotation, has a low driving voltage, and is compatible with known semiconductor electronics technologies. But, it has only single degree of freedom; rotation about an axis and two level positions. So, the micromirror array is merely the array of optical switches.
To be applied more widely, a micromirror is needed to have multi-level position control and large displacements, multi degrees of freedom motions, low driving voltage, and compatibility with known semiconductor electronics technologies.